Slip-proof block



FIG. 1 is perspective view of a slip-proof block showing my new design;

FIG. 2 is a front side elevation view thereof;

FIG. 3 is a rear side elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof. 

The ornamental design for a slip-proof block, as shown and described. 